The present invention relates to a warp shedding apparatus of a loom.
Fabrics that are used for an airbag, a parachute, and the like are woven tightly to have a high density for the specific purposes. In weaving a fabric of high density, a high tension is applied to weft yarns. In such high density fabric, weft yarns tend to be slackened and broken selvages may result at the opposite ends of the fabric in the weaving width direction.
Japanese Unexamined Patent Application Publication No. 9-302550 discloses an improved base fabric for an airbag which does not have loose weft yarns and/or broken selvages. According to the Publication, the base fabric for an airbag is made of synthetic fiber and has a selvage formed of ground yarns and leno yarns, and a plurality of processed reinforcing yarns are added to the selvage.
Generally, the end portion of a selvage in a high density fabric for an airbag may become wavy. Such wavy selvage is specific to high density fabrics and results from the local differences in the tension applied to the weft yarns, or the tension applied to the weft yarns being greater in the central portion of a woven fabric than in the portions thereof adjacent to the selvage edges on the lateral sides of the fabric. When beaten by the reed, the weft yarn becomes slack and wavy in the portions thereof adjacent to the selvage edges and the stress due to the beating is concentrated in such portions adjacent to the selvage edges, which causes irregularities in the weave structure of the above portions of the fabric adjacent to the selvage edges, resulting in defective wavy selvages. In the base fabric for an airbag disclosed in the Japanese Unexamined Patent Application Publication No. 9-302550, the force to grip the selvage edges is increased by additionally weaving reinforcing yarns to thereby prevent defective wavy selvages.
Japanese Unexamined Patent Application Publication No. 2004-232168 discloses a water jet loom having healds that are disposed outward of edges of a woven fabric in the width direction thereof and used for gripping ends of weft yarn, such as ends of selvedge yarns to be trimmed. The shed of the gripping yarns is formed by the healds mounted to either the heald frames for ground yarns or the heald frames for leno yarns. Therefore, in a loom rotating at a speed of 800 rpm or higher, a weft yarn flying in a shed tends to be directed upward under the influence of air pressure generated by beating of the reed. A weft thus diverted upward and moving away from the gripping yarns fails to be gripped, thus causing the loom to stop.
According to the Publication No. 2004-232168, the healds for holding the gripping yarns each have a thread eyelet at a position that is 5 to 15 mm higher than that of the healds for holding warp yarns. With such disposition of the thread eyelet, the raised shed opening amount of the gripping yarns is increased and a weft yarn that may fly upward is prevented successfully from being diverted away from the gripping yarns.
According to the base fabric for an airbag disclosed in the Japanese Unexamined Patent Application Publication No. 9-302550 in which a plurality of reinforcing yarns need be woven at the selvage edges of a fabric in order to prevent slackening of weft yarn and formation of wavy selvages in a high density fabric for an air bag, additional devices for supplying the reinforcing yarns are required. Such devices for supplying reinforcing yarns need have a plurality of bobbins for supplying reinforcing yarns provided in the lateral end portions of a woven fabric, which makes the configuration of the loom complicated. Furthermore, the use of bobbins for supplying the reinforcing yarns that need be replaced periodically increases the man-hour for such maintenance works.
Furthermore, according to the water jet loom disclosed in the Japanese Unexamined Patent Application Publication No. 2004-232168 in which the position of the thread eyelet for the gripping yarns that do not form a part of a woven fabric is set so that weft yarns are caught by the gripping yarns without fail. The water jet loom of the Publication No. 2004-232168 does not have any function to prevent slackening of weft yarns in the selvages or the formation of defective selvages in a fabric for airbag and the like. In particular, the gripping yarns are not required on a side of a woven fabric that corresponds to the weft insertion side of the loom. Therefore, the water jet loom disclosed in the Japanese Unexamined Patent Application Publication No. 2004-232168 is unable to prevent the slackening of weft yarns or the formation of defective selvage in a woven fabric on the side thereof that corresponds to the weft insertion side of the loom.
The present invention, which has been made in view of the above circumstances, is directed to providing a warp shedding apparatus of a loom that prevents slackening of weft yarns and formation of defective selvages in the opposite end portions of a woven fabric in the weaving width direction thereof with simple structure.